Date: Wed, 31 May 1995 11:56:00 -1000 From: mkfeil@unicad.com (Max Feil) Message-Id: <9505312131.AA29657@uniina0.unicad.com> Organization: UTexas Mail-to-News Gateway Subject: How to stop 2-line delta from PULSING? Hi folks. I bought a beginner's 2-line kite that comes completely rigged, and I was wondering how to stop it from pulsing. I flew it in pretty strong, gusty winds, and there were a few trees upwind, so the air to the kite was not totally clean, but this does not account for the divergent pitch oscillations the kite was going through! I was able to control the direction of the kite quite well, but especially when the kite was high in the sky, it started to pulse. The pulsation is one where the tension of the lines increases and decreases rapidly, and you can see the pitch angle changing with each pulse. The pulsing quickly gets so violent that I am thinking a spreader may pop off the thing! It also makes it quite unpleasant to fly. The one other 2-line kite I have flown did not do any kind of pulsing. I am going to check the lengths of the rigging lines with a ruler to make sure the two sides match, but I don't think this is it because the kite was fine directionally. There are 3 rigging lines on each side, which go to the base, the tip, and to the leading edge near the top spreader. What should I look for to determine whether the kite has been rigged correctly? I'm thinking that there is a equal rigging mistake on each side. Or perhaps this kite just needs super smooth winds? Thanks for any help! PLEASE EMAIL, SINCE I HAVE NO NEWSFEED. Regards, Max -- Max Feil | Email: max@unicad.com UniCAD (CANADA) Ltd. |------------------------------------------------------ CAD Software Development| We're "all minions to messiah Pepsi can" - Ultravox Ottawa, Ontario, Canada.| = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Thu, 1 Jun 1995 06:38:26 -1000 From: gilchgw@zoology.washington.edu (George W. Gilchrist) Message-Id: <3qkqe2$ak4@nntp4.u.washington.edu> Organization: University of Washington Subject: Re: How to stop 2-line delta from PULSING? In article <9505312131.AA29657@uniina0.unicad.com>, mkfeil@unicad.com says... > >Hi folks. I bought a beginner's 2-line kite that comes completely rigged, >and I was wondering how to stop it from pulsing. > >I flew it in pretty strong, gusty winds, ... Max, You are correct in checking the lengths of the bridle legs to make sure they match left and right. You might also try to move the tow point on the bridle towards the tail a little bit (try 1/4" increments) in higher winds (lift the nose and drop the tail). This reduces the lift on the kite, and therefore may lower the stress on the spars. In lower winds, dropping the nose (move tow point towards the nose) flattens the kite relative to the wind and increases lift. Most kites have some sort of marking on the bridle to indicate the factory setting. If yours does not, make sure you mark it with an indelible marker before changing anything!. You might also want to post the name of the kite in case someone has experience with that particular model. One other possibility is frame flex. In strong winds, lightweight spars "shudder", especially at the wingtips. This is especially true of the fiberglass spars found on less expensive kites. If this is the case, then there is no solution except to fly at lower wind speeds. This is usually more noticeable at lower elevation in the center of the wind window, however, whereas you indicate this problem is greatest at the top of the window. Do you get the same kind of pulsing at lower wind speeds? Cheers, George ============================== George W. Gilchrist gilchgw@zoology.washington.edu University of Washington Department of Zoology Box 351800 Seattle, WA 98l95-1800 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Mon, 5 Jun 1995 08:56:15 -1000 From: mkfeil@unicad.com (Max Feil) Message-Id: <9506051832.AA22320@uniina0.unicad.com> Organization: UTexas Mail-to-News Gateway Subject: Re: How to stop 2-line delta from PULSING? I wrote: > > Hi folks. I bought a beginner's 2-line kite that comes completely rigged, > and I was wondering how to stop it from pulsing. Well, I flew it again today in lighter winds in a nice open area. If anything, the pitch oscillations were worse. The kite would literally shake itself out of the sky. I think things are worse in light winds because it's harder to recover once the kite goes out of control and the lines go slack, tangle, etc, and you're history. Anyways, I experimented with changing the angle of attack of the kite by changing the lengths of bridle lines, but this did not improve anything. The pitch angle of the kite seems fine. Directional control is also fine, except of course once the kite shakes itself out of control. I was wondering how important the center of gravity (CG) is for a kite? In the world of airplanes that I'm more familiar with, the center of gravity is the main parameter determining pitch stability. Would a CG that is not forward enough cause this kind of problem on a kite? It sure would on an airplane. What is the rule of thumb for CG location in kite design? In airplane design, the rule of thumb is "CG should be in front of the aerodynamic center of the entire airplane by a static margin of between 5 and 15 percent MAC (Mean Aerodynamic Chord)". I'm sure the bridle factors into the CG equation as well. Could the effective towing point be in the wrong place wrt. the CG? Wrt the aerodynamic center? Is there an effective towing point with 3 bridle lines? It must change an awful lot with the tension on the bridle (the lines alternate going slack). Input from kite designers out there would be appreciated. By the way, my kite is called the "Blaster" made by "Touch the Sky". Please no flames about buying a $40 kite. The kite has already given me all the flames I can handle! Regards, Max -- Max Feil | Email: max@unicad.com UniCAD (CANADA) Ltd. |------------------------------------------------------ CAD Software Development| We're "all minions to messiah Pepsi can" - Ultravox Ottawa, Ontario, Canada.| = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Tue, 6 Jun 1995 05:38:34 -1000 From: gilchgw@zoology.washington.edu (George W. Gilchrist) Message-Id: <3r1spq$l7p@nntp4.u.washington.edu> Organization: University of Washington Subject: Re: How to stop 2-line delta from PULSING? In article <9506051832.AA22320@uniina0.unicad.com>, mkfeil@unicad.com says... >Input from kite designers out there would be appreciated. By the way, >my kite is called the "Blaster" made by "Touch the Sky". Please no >flames about buying a $40 kite. The kite has already given me all the flames >I can handle! Max, If I were you, I would take or send the kite back to where I bought it (assuming that it is relatively new). It sounds like you got a lemon; most reputable dealers will stand behind what they sell. Cheers, George -- ============================== George W. Gilchrist gilchgw@zoology.washington.edu University of Washington Department of Zoology Box 351800 Seattle, WA 98l95-1800 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =